Both sides currently occupy the top six. Bristol City are defying their expectations for the season under Dean Holden, they are third in the table and remain in good form. They have won their last three games including a late victory over bottom club Derby County at the weekend.
Watford will be pleased they are in touching distance of the top two after their relegation last season.
They sit fifth in the Championship, a point behind their opponents and Bournemouth, who are second.
Vladimir Ilic's side played out a disappointing 1-1 draw with strugglers QPR on Saturday, they are bound to want to prove a point on Wednesday.
Bristol City's tremendous start to the campaign is amplified when you consider their injury woes.
Dean Holden is without six key first-team players, some for a considerable amount of time. Alfie Mawson, Andreas Weimann and Nathan Baker are all out for the long term, with knee, ACL, and hamstring injuries respectively.
Steven Sessegnon is also out and he's not due back until the new year. The consolation for The Robins is that Liam Walsh and Joe Williams aren't far off making a return.
Famara Diedhiou may earn a start after he scored the late winner against Derby from the bench.
Watford midfielder Tom Cleverley is doubtful to feature after he missed the draw with QPR. So too is Christian Kabasele, meaning Ilic will be without two key starting players for what will be a big clash.
Neither side are missing any players through suspension.
Bristol City (4-3-3)
Bentley; Hunt, Vyner, Kalas, Dasilva; Paterson, Nagy, Bakinson; Semenyo, Wells, Diedhiou.
Foster; Cathcart, Troost-Ekong, Wilmot; Femenia, Garner, Capoue, Chalobah, Seba; Pedro, Sarr.
Ones to watch
Jamie Paterson has been a revelation for Bristol City under Dean Holden. Last season under Lee Johnson, the midfielder was told he had no future, subsequently leaving on loan to Derby.
However, upon return, he forced his way back into the side and hasn't looked back. This season, he has scored three goals and provided two assists already.
But it is his athleticism and willingness to run which makes him stand out. He is great at linking the midfield and attack, while his late runs into the box are always a threat.
Many were shocked when Ismaila Sarr didn't leave Watford in the latest transfer window. He was subject of links to both Liverpool and Manchester United, but nothing materialised and he remains at Vicarage Road.
He has taken the Championship by storm so far, instilling fear in opposition defenders by just the sight of him dribbling. The 22-year-old may only have scored three and assisted one, but it is clear that these numbers will rise.
Sarr takes 2.9 shots per game, which indicates that he is getting into good spaces often in games. His 2.2 dribbles per 90 indicates what we already knew about him - he loves taking on defenders. Bristol City's back four must be on top form to keep him quiet.
Wednesday will be the first league meeting between these two since 2013, when relegation-threatened City defeated Watford 2-0.
Since then, there have been four cup meetings. A 1-1 draw in the FA Cup lead to a Watford replay victory, whilst Bristol City beat Watford in the 2017 League Cup on the way to the semi-final.
How to watch
Bristol City vs Watford is available to watch on Sky Sports Football. Coverage begins at 19:15, in preparation for a 19:45 kick-off BST.